The 3rd Generation Partnership Project (3GPP), which is a standardization project, standardized the Evolved Universal Terrestrial Radio Access (hereinafter referred to as the “E-UTRA”), in which high-speed communication is realized by adopting an Orthogonal Frequency-Division Multiplexing (OFDM) communication scheme and flexible scheduling using a unit of prescribed frequency and time called resource block.
Moreover, the 3GPP discusses the Advanced E-UTRA, which realizes higher-speed data transmission and has upper compatibility with the E-UTRA. The E-UTRA relates to a communication system based on a network in which base station devices have substantially the same cell configuration (cell size); however, regarding the Advanced E-UTRA, discussion is made on a communication system based on a network (different-type radio network, Heterogeneous Network) in which base station devices (cells) having different configurations coexist in the same area. The E-UTRA is also referred to as the “Long Term Evolution (LTE)”, and the Advanced E-UTRA is also referred to as the “LTE-Advanced”. The LTE may be a general term including the LTE-Advanced.
A carrier aggregation (CA) technique and a dual connectivity (DC) technique are defined, in which, in a communication system where cells (macro cells) having large cell radii and cells (small cells) having smaller cell radii than those of the macro cells coexist as in a heterogeneous network, a terminal device performs communication by connecting to a macro cell and a small cell at the same time (NPL 1).
On the other hand, discussion is made on Licensed-Assisted Access (LAA) in NPL 2. In the LAA, an Unlicensed spectrum used in a wireless Local Area Network (LAN) is used as the LTE, for example. Specifically, the Unlicensed spectrum is configured as a Secondary cell (secondary component carrier). The Secondary cell used as the LAA is assisted regarding connection, communication, and/or configuration by a Primary cell (primary component carrier) configured in a Licensed spectrum. The LAA extends a spectrum available to the LTE, allowing broadband transmission. The LAA is also used in a shared spectrum which is shared between predetermined operators.
Moreover, latency in radio communication is one of critical factors in a system aiming at ensuring security and reliability. For the LTEs including the LTE using the LAA and the LTE of the related art using a Licensed spectrum, it is important to further reduce latency.